The following relates to the lighting and display arts. It especially relates to active matrix liquid crystal display (LCD) devices, and will be described with particular reference thereto. However, it will also find application in other types of LCD displays, and in other types of backlit display devices.
With reference to FIG. 1, a conventional flat screen display 10 includes an active matrix liquid crystal display (LCD) 12 and a backlight 14. The LCD 12 includes a matrix of thin film transistors (TFTs) 16 fabricated on a substrate 18 of glass or another transparent material. A liquid crystal film 20 is disposed over the substrate 18 and the TFTs 16. Addressing of the TFTs 16 by gate lines (not shown) deposited on the substrate 18 during TFT fabrication cause selected TFTs 16 to conduct electrical current and charge the liquid crystal film 20 in the vicinity of the selected TFTs 16. Charging of the liquid crystal film 20 alters the opacity of the film, and effects a local change in light transmission of the liquid crystal film 20. Hence, the TFTs 16 define display cells or pixels 22 in the liquid crystal film 20. Typically, the opacity of each pixel 22 is charged to one of several discrete opacity levels to implement an intensity gray scale, and so the pixel 22 is a gray scale pixel. However, pixel opacity also can be controlled in a continuous analog fashion or a digital (on/off) fashion.
A color-selective filter 26, 28, 30 is disposed over each pixel 22. Specifically, first color filters 26 of a first color component, second color filters 28 of a second color component, and third color filters 30 of a third color component are distributed on pixels 22 across the display area of the LCD 12 to produce a color display. Typically, the first, second, and third colors include red, green, and blue primary colors to produce a red-green-blue (RGB). Preferably, a top matrix 32 of opaque lines separating pixels 22 is arranged between the color filters 26, 28, 30 to improve visual contrast. Specifically, FIG. 1 shows a single color or RGB pixel that includes a first component color (e.g., red output by the pixel 22 covered by the filter 26), a second component color (e.g., green output by the pixel 22 covered by the filter 28), and a third component color (e.g., blue output by the pixel 22 covered by the filter 30) that are selectively combined or blended to generate a selected color.
In operation, the backlight 14, which includes a white compact fluorescent lamp (CFL), an array of white light emitting diodes (LEDs), or other white light source 34, produces a substantially uniform white planar illumination directed toward the LCD 12. A polarizer 36 of the LCD 12 disposed on a backside of the substrate 18 optimizes the light polarization with respect to polarization properties of the liquid crystal film 20. The opacity of the pixels 22 is modulated using the TFTs 16 as discussed previously to create a transmitted light intensity modulation across the area of the display 10. The color filters 26, 28, 30 colorize the intensity-modulated light emitted by the pixels to produce a color output. By selective opacity modulation of neighboring pixels 22 of the three color components, selected intensities of the three component colors (e.g., RGB) are blended together to selectively control color light output. The pixels 22 of a particular color or RGB pixel such as that shown in FIG. 1 are blended. As is known in the art, selective blending of three primary colors such as red, green, and blue can generally produce a full range of colors suitable for color display purposes. Spatial dithering is optionally used to provide further color blending across neighboring color pixels.
Conventional flat screen displays such as the exemplary display 10 suffer certain disadvantages. The light output efficiency is poor due to light absorption within the LCD 12. Typically, the polarizer 36 reduces the light intensity by about 50%. The TFTs 16 produce further shadow losses of a magnitude dependent upon the TFT device area. Typical losses due to TFT shadowing in present active matrix liquid crystal displays are about 115%. The color filters 26, 28, 30 each substantially absorb two of the three color components to produce a pure third color component output, and hence have transmissivities no higher than about 30%. Combining these losses, the light output efficiency for the LCD 12 is about 5%.
Another disadvantage of conventional LCD-based flat screen displays is manufacturing complexity. In particular, for each gray scale pixel 22 one of the color filters 26, 28, 30 is precisely aligned and bonded. Precision in the filter alignment is critical since misalignment can create gaps through which white light can pass. This alignment process is time-consuming and error-prone.
Yet another disadvantage of conventional LCD-based flat screen displays is a relatively large color (RGB) pixel size since each color pixel is comprised of at least three component gray scale pixels 22. In some arrangements, a second green pixel is included to compensate for visual color sensitivity differences, leading to a still larger color pixel size. Increased color pixel size corresponds to reduced display resolution.
The following contemplates an improved apparatus and method that overcomes the above-mentioned limitations and others.